A number of diagnostic and interventional vascular procedures are now performed transluminally, where a catheter is introduced to the vascular system at a convenient access location and guided through the vascular system to a target location using established techniques. Such procedures require vascular access which is usually established using the well known Seldinger technique, as described, for example, in William Grossman's "Cardiac Catheterization and Angiography," 3rd Ed., Lea and Febiger, Philadelphia, 1986, incorporated herein by reference.
When vascular access is no longer required, the introducer sheath must be removed and bleeding at the puncture site stopped. One common approach to attempt providing hemostasis (the cessation of bleeding) is to apply external force near and upstream from the puncture site, typically by manual or "digital" compression. This approach suffers from a number of disadvantages. It is time-consuming, frequently requiring one-half hour or more of compression before hemostasis is assured. This procedure is uncomfortable for the patient and frequently requires administering analgesics to be tolerable. Moreover, the application of excessive pressure can at times totally occlude the underlying blood vessel, resulting in ischemia and/or thrombosis. Following manual compression the patient is required to remain recumbent for at least six and at times as long as eighteen hours under close observation to assure continued hemostasis. During this time renewed bleeding may occur resulting in bleeding through the tract, hematoma and/or pseudoaneurism formation as well as arteriovenous fistula formation. These complications may require blood transfusion and/or surgical intervention. The incidence of these complications increases when the sheath size is increased and when the patient is anti-coagulated. It is clear that the standard technique for arterial closure can be risky, and is expensive and onerous to the patient. While the risk of such conditions can be reduced by using highly trained individuals, such use is both expensive and inefficient.
To overcome the problems associated with manual compression, the use of bioabsorbable fasteners to stop bleeding has been proposed by several groups. Generally, these approaches rely on the placement of a thrombogenic and bioabsorbable material, such as collagen, at the superficial arterial wall over the puncture site. While potentially effective, this approach suffers from a number of problems. It can be difficult to properly locate the interface of the overlying tissue and the adventitial surface of the blood vessel, and locating the fastener too far from that surface can result in failure to provide hemostasis and subsequent hematoma and/or pseudo aneurism formation. Conversely, if the fastener intrudes into the arterial lumen, intravascular clots and/or collagen pieces with thrombus attached can form and embolize downstream causing vascular occlusion. Also, thrombus formation on the surface of a fastener protruding into the lumen can cause a stenosis which can obstruct normal blood flow. Other possible complications include infection as well as adverse reactions to the collagen implant.
Catheters are also used to treat heart disease which is a major medical ailment wherein arteries become narrowed or blocked with a build-up of atherosclerotic plaque or clot which reduces flow to tissues downstream or "distal" to the blockage. When this flow reduction becomes significant, a patient's quality of life may be significantly reduced. In fact, heart disease patients often die when critical arteries, such as the coronary arteries, become significantly blocked.
However, technology has been developed to open some blocked arteries in the treatment of heart disease. For example, balloon angioplasty has become a well accepted treatment wherein a balloon is inflated within the narrowed vessel to stretch or otherwise deform the blockage into a larger lumen. Alternatively, the blockage can even be removed, such as in a procedure known as atherectomy. In general, these treatments use percutaneous catheters which are inserted into the patients' vessels at a peripheral artery or vein puncture site and guided to the internal blockage site via x-ray visualization. The blockage is then treated remotely by use of hydraulic pressure in the case of balloon angioplasty, or by other actuating means to cause remote cutting or ablation of the blockage in the case of atherectomy.
Coronary Artery Bypass Graft Surgery ("CABG")
In the alternative to using catheters to treat heart disease, or when such catheterizations are contraindicated, some blocked vessels can be treated with coronary artery bypass graft surgery ("CABG"). In conventional CABG techniques, a tubular graft is affixed to a port or aperture in an artery wall distally of the blockage. When the opposite end of the tube is in fluid communication with a pressurized arterial blood supply, such as the aorta, the tubular graft provides a conduit for flow into the vessel lumen distally of the blockage.
Conventional CABG surgery is generally initiated by directly exposing the heart to the surgeon. This is accomplished by opening the patient's chest using known sternotomy and retraction techniques that cut the sternum and spread the rib cage open. Then, one or both lungs are usually deflated and the patient is connected to a respiratory assist machine.
Once the heart is exposed, the patient is connected to a coronary bypass machine so that the blood supply circumvents the heart. In this way, the heart is depressurized so that apertures can be cut into the walls of the vessels for surgical graft attachment. The right atrium (or vena cava) and the aorta each is intubated with cannulas which are connected to an artificial pump and oxygenator. Once these major vessels are cannulated, cardioplegia is delivered to slow or stop the beating motion of the heart. The aorta is then clamped proximally of the aortic bypass cannula, thereby isolating the proximal aortic root from the blood that is being circulated by the bypass machine.
After the heart is isolated from blood pressure, conventional bypass grafting is performed. The required grafts are implanted to feed the coronary arteries distal to the blockage, the clamp is removed from the aorta, the lungs are restored, and the patient is then taken off of the bypass pump.
In one type of CABG method, the bypass grafting is achieved between the aorta and one of the three major coronary arteries or their sub-branches, the left anterior descending artery (LAD), the circumflex artery (CIRC), or the right coronary artery (RCA). In such a case, a saphenous vein is usually taken from the patient's leg and is transplanted as a "homograft" to connect these vessels in the same patient's chest. Artificial grafts have also been disclosed as providing potential utility for this purpose and are herein collectively included in the general discussion of "saphenous veins" as used in CABG procedures.
An alternative CABG method uses the internal mammary artery (IMA) alone or in conjunction with the saphenous vein graft. The IMA is severed at a chosen location and is then connected to an aperture, in a coronary artery.
In either case of using saphenous vein homografts or artificial grafts in CABG surgery, the proximal end of the graft is generally sutured or otherwise is affixed circumferentially to the tissue surrounding an aperture that is punched into the wall of the aorta. In this arrangement, the lumen of the graft communicates with the vessel through the aperture, wherein ideally the aperture approximates the inner diameter of the graft lumen. The opposite, distal end of the graft is sutured to an aperture formed in the wall of the coronary vessel distal to the blockage.
The fluid connections between a graft and a vessel are herein referred to as "anastomoses." In the instance of CABG, "proximal anastomoses" and "distal anastomoses" are terms used when referring to grafting to the aorta and the coronary artery, respectively. In most CABG procedures using saphenous vein grafts, the distal anastomosis is performed first, followed by the proximal anastomosis.
For the CABG method using the IMA, only one distal anastomosis is formed distal to the arterial blockage. A proximal anastomosis to the aorta is not required as it is in a saphenous vein graft procedure because the IMA's natural arterial blood flow feeds the heart.
In conventional CABG surgery methods such as those just summarized, the timing and technique of the anastomosis procedures are critical factors to procedural success. In fact, it is believed that three critical determinants which affect outcomes of CABG surgery are: (1) time the patient spends on bypass, (2) time the patient spends with a clamped aorta, and (3) the quality of the anastomoses. It is generally believed that a CABG patient's operative and peri-operative morbidity are directly related to how long the patient must be on heart bypass. In fact, it is generally understood that the risk of patient morbidity is believed to rise significantly after a threshold time of one hour on bypass. Perhaps the most prevalent complication arising from prolonged cardiac bypass is the high risk of distal thrombus created by the artificial plumbing. For example, such thrombi can embolize into the neurovasculature and potentially can cause a stroke. In analyzing the timing of individual CABG steps against the backdrop of a patient's critical time on bypass, the time spent anastomosing the grafts to vessels emerges as a controlling factor. The average time for suturing one anastomosis is approximately 7-10 minutes. Furthermore, it is believed that an average CABG procedure involves approximately five anastomoses: two saphenous vein grafts, each with a proximal and a distal anastomosis, and one internal mammary artery having only one distal anastomosis. Therefore, the average time for graft suturing ranges from 35 minutes to 50 minutes--in any case a significant portion of the 60 minute critical threshold to patient morbidity. Closely related to the time spent on bypass is a second CABG success factor related to the extent and time of aortic cross-clamping. It is believed that the inherent crushing force from a cross-clamp across the bridge of the muscular aortic arch may be associated with a high degree of tissue trauma and structural damage. Additionally, hemostasis formed at or adjacent to the cross clamp, perhaps in conjunction with the tissue trauma of clamping, may also be a source of unwanted thrombogenesis.
In addition to the timing of anastomosing grafts and extent and duration of aortic cross-clamping, the quality of interface between the graft and vessel is also believed to be an indicator of procedural success. The accuracy, trauma, and repeatability of suturing, as well as the three-dimensional interface formed between the conduits at the anastomosis site, are significant variables in conventional manual surgical techniques. These variables are believed to significantly affect the short or long-term success of conventional CABG anastomosis procedures.
Limitations of Conventional CABG Devices & Methods
Both of the critical CABG success indicators summarized above--time on cardiac bypass and quality of anastomosis suturing--are directly affected by inherent limitations in the devices used in conventional CABG procedures. It is believed that improvements to these devices and related methods of use may provide for more rapid and reliable vessel-graft anastomosing. For example, conventional "surgical punches" are devices that cut or "punch" a plug in vessel wall tissue to form an aperture in the wall. In a CABG procedure, the tissue surrounding a punched-out aperture provides the substrate upon which a graft may be sutured to form an anastomosis. One procedural limitation in using conventional surgical punches is that hemostasis can not be maintained at a vessel wall after a plug of tissue is punched out and removed. Therefore, an aperture in an aortic wall during a saphenous vein graft procedure can only be made when that portion of the aorta is cross-clamped, bypassed, and depressurized. Otherwise, the high blood pressure and flow in the aorta would cause significant bleeding during the period from punching the aperture to forming the anastomosis. Because of this limitation in conventional surgical punches, the threshold 60 minute coronary bypass clock begins running before punching the aorta.
The prior art fails to disclose or fulfill the need which exists in the field of medical devices and methods for: suturing tissue by proximally drawing sutures through a tissue layer in the proximity of an aperture; suturing vascular tissue while maintaining adequate perfusion or hemostasis, or both; a medical device assembly or surgical method that allows for a graft to be anastomosed to an aperture in a vessel wall while maintaining hemostasis at the anastomosis with physiological flow and/or pressure in the vessel lumen; a surgical punch assembly that punches and removes tissue to form an aperture in a vessel wall while maintaining hemostasis at the aperture with physiological flow and/or pressure in the vessel lumen; a cannula that includes a tube and a hemostatic valve that slideably receives an elongated medical device which is radially removable from the tube and hemostatic valve; a medical device assembly that automatically and repeatably places suture thread through vessel wall tissue surrounding an aperture in the vessel wall in a suture pattern that is useful for anastomosing a tubular graft to the aperture; and a medical device assembly that deploys a suture with one end extending through the tissue that surrounds a punched aperture in a vessel wall and the opposite suture end extending radially through a tubular graft wall adjacent an open end of the graft, such that a vessel anastomosis may be rapidly and repeatably performed in a CABG procedure even while the vessel is under physiological flow.